(* 9. Pierce 7.3.1 *)

(* This replaces existing eval function in untypes/core.ml *)

let rec eval ctx t = match t with
    _ when isval ctx t -> t
  | TmApp(fi,t1,t2) ->
      (match eval ctx t1 with
	 TmAbs(_,_,t12) ->
	   eval ctx (termSubstTop (eval ctx t2) t12)
       | _ -> raise NoRuleApplies)
  | _ -> raise NoRuleApplies